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Abstract:

Packaged capacitive devices are described having electrical interconnects
of electrodes which possess efficient electrical contact between current
collectors, electrical isolation of electrodes, and/or electrochemical
stability, while minimizing the mechanical stress and strain applied to
the electrodes, in part, due to the use of a compliant layer. The
packaged capacitive devices are adaptable to a wide range of electrode
diameters and electrode stack lengths.

Claims:

1. A packaged capacitive device comprisinga linear stack comprising two or
more electrodes arranged in series;at least two current collectors, each
in electrical contact with one or more electrodes in the linear stack,
wherein electrodes in electrical contact with one current collector are
insulated from electrical contact with another current collector; anda
compliant layer enclosing the linear stack and current collectors,
wherein the compliant layer is under circumferential tensile stress and
applies radial compressive stress to the linear stack and current
collectors to ensure electrical contact between the current collectors
and respective electrodes in the linear stack.

2. The packaged capacitive device according to claim 1, wherein the
compliant layer is selected from a heat shrink thermoplastic polymer, an
elastomer and combinations thereof.

3. The packaged capacitive device according to claim 2, wherein the heat
shrink thermoplastic polymer is selected from a polyolefin, a
fluoropolymer, a poly (vinyl chloride), a neoprene, a silicone, a
fluoroelastomer and combinations thereof.

4. The packaged capacitive device according to claim 2, wherein the
elastomer is selected from a saturated rubber, an unsaturated rubber, a
thermoplastic, a thermoplastic vulcanizate, a polyurethane rubber, a
polysulfide rubber and a combination thereof

5. The packaged capacitive device according to claim 1, wherein the
compliant layer is in a form selected from a sleeve, a tube, a wrapped
sheet and a combination thereof.

6. The packaged capacitive device according to claim 1, further comprising
a first fluidic plug adjacent to a first end of the linear stack and a
second fluidic plug adjacent to a second end of the linear stack.

7. The packaged capacitive device according to claim 6, wherein the first
fluidic plug comprises an inlet for receiving a fluid and the second
fluidic plug comprises an outlet for discharging at least a portion of
the fluid received by the inlet.

8. The packaged capacitive device according to claim 6, wherein the first
fluidic plug and the second fluidic plug are sealed to the linear stack
by the compliant layer.

9. The packaged capacitive device according to claim 1, wherein the linear
stack is cylindrical.

10. The packaged capacitive device according to claim 1, wherein each
electrode in the linear stack is a flow-through electrode.

11. The packaged capacitive device according to claim 10, wherein each
electrode comprises a plurality of inner channels having surfaces defined
by porous walls and extending through the electrode from a first face to
an opposing second face.

12. The packaged capacitive device according to claim 10, wherein the
electrode material for each electrode is selected from a carbon, a
carbon-based composite, a carbon-based laminate, a conductive metal
oxide, a conductive polymer and combinations thereof.

14. The packaged capacitive device according to claim 13, wherein the
current collectors are in the form of a compliant sheet.

15. The packaged capacitive device according to claim 1, further
comprising a rigid outer housing enclosing the linear stack, the current
collectors, and the compliant layer.

16. The packaged capacitive device according to claim 15, further
comprising at least one reinforcing rib disposed between the linear stack
and the rigid outer housing.

17. The packaged capacitive device according to claim 16, wherein the
reinforcing rib material is selected from a structural polymer, a metal,
a ceramic, and a combination thereof.

18. The packaged capacitive device according to claim 16, comprising two
or more reinforcing ribs axially disposed to the compliant layer.

19. A method of making a packaged capacitive device, the method
comprising:providing a linear stack comprising two or more electrodes
arranged in series;providing at least two current collectors, each in
contact with one or more electrodes in the linear stack, wherein
electrodes in contact with one current collector are insulated from
contact with another current collector; andapplying a compliant layer
enclosing the linear stack, and the current collectors.

20. The method according to claim 19, wherein applying the compliant layer
comprises diametrically expanding an elastomeric housing, positioning it
around the linear stack and the current collectors, and removing the
expanding forces and allowing the compliant layer to contract to apply
radial and axial compressive forces to the linear stack and current
collectors.

21. The method according to claim 20, wherein allowing the compliant layer
to contract to apply radial and axial compressive forces to the linear
stack and current collectors comprises applying heat to the compliant
layer such that the compliant layer shrinks and conforms to the shape of
the linear stack and the current collectors.

22. The method according to claim 19, further comprising attaching a first
fluidic plug adjacent to a first end of the linear stack and a second
fluidic plug adjacent to a second end of the linear stack.

23. The method according to claim 22, wherein the first fluidic plug
comprises an inlet for receiving a fluid and the second fluidic plug
comprises an outlet for discharging at least a portion of the fluid
received by the inlet.

Description:

BACKGROUND

[0001]1. Field of the Invention

[0002]The present invention relates generally to a packaged capacitive
device and more particularly to a packaged capacitive device useful for
capacitors and/or for capacitive deionization.

[0003]2. Technical Background

[0004]Capacitors, like batteries, store energy in the electrical field
between a pair of oppositely charged conductive plates. Developed more
than 250 years ago, capacitors are frequently used in electrical circuits
as energy storage devices. In recent years, new families of capacitive
devices have been developed which are based on charge separation of ions
in solution and the formation of electrical double layers.

[0005]An electric double layer capacitor (EDLC) is an example of a
capacitor that typically contains porous carbon electrodes (separated via
a porous separator), current collectors and an electrolyte solution. When
electric potential is applied to an EDLC cell, ionic current flows due to
the attraction of anions to the positive electrode and cations to the
negative electrode. Electric charge is stored in the electric double
layer (EDL) formed along the interface between each polarized electrode
and the electrolyte solution.

[0006]EDLC designs vary depending on application and can include, for
example, standard jelly roll designs, prismatic designs, honeycomb
designs, hybrid designs or other designs known in the art. The energy
density and the specific power of an EDLC can be affected by the
properties thereof, including the electrode and the electrolyte utilized.
With respect to the electrode, high surface area carbons, carbon
nanotubes, activated carbon and other forms of carbon and composites have
been utilized in manufacturing such devices. Of these, carbon based
electrodes are used in commercially available devices.

[0007]Capacitive Deionization (CDI) is a promising deionization
technology, for instance, for the purification of water. In this context,
positively and negatively charged electrodes are used to attract ions
from a stream or bath of fluid. The ions form electric double layers on
the surfaces of the electrodes, which are fabricated from some form of
high surface area material, for example, a form of activated carbon.
After interaction with the electrodes during the charging period, the
fluid contains a lower overall ion content and is discharged. A volume of
purge fluid is then introduced to the electrodes. The electrodes are then
electrically discharged, thus releasing the trapped ions into the purge
fluid. The purge fluid is then diverted into a waste stream and the
process repeated.

[0008]Electrically connecting electrodes to a power source is a
challenging aspect for EDLC and CDI applications. Typically, electrodes
are delicate, thus mechanical stressing and straining of the electrodes
should be minimized. Minimizing the deformations applied to the
electrodes is difficult, especially while attempting to maximize the
electrical and mechanical integrity of an electrical interconnect to the
electrodes.

[0009]U.S. Pat. No. 5,954,937 relates to an interconnection for
resorcinol/formaldehyde carbon aerogel/carbon paper sheet electrodes. The
fluid flow path is located between the surfaces of the electrode sheets.
The active surfaces of these electrode sheets are delicate and should be
protected from mechanical stressing. The electrode sheets are bonded to a
current collector, in this case, a titanium sheet using a conductive
carbon filled adhesive. The large area of contact between the electrode
sheet and the current collector insure relatively low overall resistance
despite the moderately high resistivity of the adhesive interface.

[0010]U.S. Pat. No. 6,778,378 relates to electrodes which may be rolled
from carbon and fibrillated polytetrafluoroethylene (PTFE). Electrodes
formed in this fashion are thin flexible sheets which can be contacted by
high normal compressive forces. Electrodes may be stacked up with sheets
of current collector material and a separator material and then clamped
with a compressive force to obtain good electrical contact. By
controlling which electrodes and current collectors are in physical
contact, a capacitive cell may be formed.

[0011]A flow-through (rather than parallel plate) flow geometry is
described in commonly owned U.S. Pat. No. 6,214,204. In this reference,
monolithic, low back pressure porous electrodes are made by one of
several methods, which include honeycomb extrusion, casting or molding
from a phenolic resin-based batch. After curing, these parts are
carbonized and activated to create high surface area carbon monoliths
with good electrical conductivity.

[0012]Discs are made and assembled in a stack and spaced such that the
discs are electrically isolated from each other. The discs are connected
to anode and cathode current collector/bus bar assemblies utilizing
wires.

[0013]A variety of other approaches of electrically interconnecting
electrodes and packaging the electrodes to form packaged devices have
been considered in the art with one or more disadvantages as described
below. Brazing or soldering alloys typically will not withstand either
the EDLC or the CDI electrochemical environments. Brazing and/or
soldering to carbon is difficult due, in part, to the low strength of
activated carbon. Conductive adhesives formulated using highly conductive
metal powders are costly and/or are prone to corrosion. Conductive
adhesives formulated using carbon powders generally have insufficient
electrical conductivity for use in a capacitor.

[0014]Conductive wire or strip leads mechanically fastened around the
perimeter of a capacitive device provide adequate performance for small
electrodes. However the resistive losses introduced by conducting charge
around the circumference of the electrode in a small diameter wire or
thin strip lead degrade performance, and no simple means has been found
to use this attachment scheme while incorporating a high efficiency
current collector. Also, the logistics of attaching leads to individual
electrodes are not appealing.

[0015]Further, packaging the resulting interconnected electrodes is
challenging due, in part, to the typical packaging materials being rigid
materials which can compromise the mechanical integrity of the
electrodes.

[0016]It would be advantageous to develop a packaged capacitive device
comprising interconnected electrodes which are capable of non-impeded
fluid flow through the electrodes, which is useful for, for example, CDI.
Further, it would be advantageous to have a packaged capacitive device
wherein the packaging enhances the electrical interconnect to a linear
stack of monolithic high surface area carbon electrodes and does not
jeopardize the mechanical integrity of the electrodes. Also, it would be
advantageous to have the methods of packaging a capacitive device provide
a reduction in processing steps and a cost reduction in the manufacturing
process.

SUMMARY

[0017]One embodiment of the invention is a packaged capacitive device
comprising a linear stack comprising two or more electrodes arranged in
series. At least two current collectors are each in electrical contact
with one or more electrodes in the linear stack. The electrodes in
electrical contact with one current collector are insulated from
electrical contact with another current collector. A compliant layer
encloses the linear stack and current collectors. The compliant layer is
under circumferential tensile stress and applies radial compressive
stress to the linear stack and current collectors to ensure electrical
contact between the current collectors and respective electrodes in the
linear stack.

[0018]Another embodiment of the invention is a method of making a packaged
capacitive device. The method comprises providing a linear stack
comprising two or more electrodes arranged in series, providing at least
two current collectors, each in contact with one or more electrodes in
the linear stack, wherein electrodes in contact with one current
collector are insulated from contact with another current collector, and
applying a compliant layer enclosing the linear stack, and the current
collectors.

[0019]The packaged capacitive device according to the invention provides
one or more of the following advantages: efficient electrical contact,
good electrical isolation, and good electrochemical stability, while
requiring a very modest level of stress be applied to the electrodes. The
packaging for the capacitive device is readily adaptable to a wide range
of electrode diameters and linear stack lengths.

[0020]Additional features and advantages of the invention will be set
forth in the detailed description which follows, and in part will be
readily apparent to those skilled in the art from the description or
recognized by practicing the invention as described in the written
description and claims hereof, as well as the appended drawings.

[0021]It is to be understood that both the foregoing general description
and the following detailed description are merely exemplary of the
invention, and are intended to provide an overview or framework for
understanding the nature and character of the invention as it is claimed.

[0022]The accompanying drawings are included to provide a further
understanding of the invention, and are incorporated in and constitute a
part of this specification. The drawings illustrate one or more
embodiment(s) of the invention and together with the description serve to
explain the principles and operation of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023]The invention can be understood from the following detailed
description either alone or together with the accompanying drawing
figures.

[0024]FIG. 1 is an exploded view schematic of a packaged capacitive device
according to one embodiment of the invention.

[0025]FIG. 2A is a cross-sectional schematic of a packaged device
according to one embodiment of the invention.

[0026]FIG. 2B is a cross-sectional schematic of a packaged device
according to one embodiment of the invention.

[0027]FIG. 3 is a photograph of a packaged device according to one
embodiment of the invention.

[0028]FIG. 4 is a photograph of a packaged device according to one
embodiment of the invention.

DETAILED DESCRIPTION

[0029]Reference will now be made in detail to various embodiments of the
invention, examples of which are illustrated in the accompanying
drawings. Wherever possible, the same reference numbers will be used
throughout the drawings to refer to the same or like parts.

[0030]One embodiment of the invention, as shown by the exploded view
schematic in FIG. 1, is a packaged capacitive device 100 comprising a
linear stack 10 comprising two or more electrodes 12 arranged in series.
At least two current collectors 13 and 14 are each in electrical contact
with one or more electrodes in the linear stack. The electrodes in
electrical contact with one current collector are insulated from
electrical contact with another current collector as shown by feature 18
in FIG. 2A and FIG. 2B. A compliant layer 16 encloses the linear stack
and current collectors. The compliant layer is under circumferential
tensile stress and applies radial compressive stress to the linear stack
and current collectors to ensure electrical contact between the current
collectors and respective electrodes in the linear stack.

[0031]According to one embodiment, the compliant layer is selected from a
heat shrink thermoplastic polymer, an elastomer and combinations thereof.
When the compliant layer is a heat shrink thermoplastic polymer,
according to some embodiments, the heat shrink thermoplastic polymer is
selected from a polyolefin, a fluoropolymer, a Poly(vinyl chloride)
(PVC), a neoprene, a silicone, a fluoroelastomer, for example,
Viton®, available from Dupont and combinations thereof. According to
some embodiments, when the compliant layer is an elastomer, the elastomer
is selected from a saturated rubber, an unsaturated rubber, a
thermoplastic, a thermoplastic vulcanizate, a polyurethane rubber, a
polysulfide rubber and a combination thereof. According to one
embodiment, the compliant layer is in a form selected from a sleeve, a
tube, a wrapped sheet and a combination thereof.

[0032]In a packaged capacitive device, according to one embodiment, the
linear stack is cylindrical and each electrode has a circular perimeter.
According to other embodiments, the electrodes and subsequently, the
linear stack can be, for example, polygonal, circular, cylindrical,
square, cubed, triangular, pentagonal, hexagonal or a combination
thereof.

[0033]Each electrode in the linear stack, in one embodiment, is a
flow-through electrode. Each electrode can comprise a plurality of inner
channels having surfaces defined by porous walls and extending through
the electrode from a first face to an opposing second face, for example,
each electrode can be in the form of a honeycomb monolith. According to
one embodiment, the electrode material for each electrode is selected
from a carbon, a carbon-based composite, a carbon-based laminate, a
conductive metal oxide, a conductive polymer and combinations thereof.

[0034]According to one embodiment, the current collectors are,
independently, a material selected from nickel, carbon, graphite,
titanium, aluminum, nickel, copper, silver, gold, platinum and
combinations thereof. The current collectors can be in the form of a
compliant sheet.

[0035]As shown by the cross-sectional schematics in FIG. 2A and FIG. 2B,
the packaged capacitive device 200 and 201 respectively, according to
some embodiments, further comprises a rigid outer housing 22 enclosing
the linear stack comprising two or more electrodes 12, the current
collectors 13 and 14, and the compliant layer 16. The rigid outer housing
can provide additional mechanical protection and may also provide
additional mechanical pressure to enhance the electrical contact within
the capacitive device.

[0036]According to some embodiments, as shown in FIG. 1, FIG. 2A and/or
FIG. 2B, the packaged capacitive device further comprises at least one
reinforcing rib 20 disposed between the linear stack comprising two or
more electrodes 12 and the rigid outer housing 22. The packaged
capacitive device, in some embodiments, comprises two or more reinforcing
ribs axially disposed to the compliant layer. In one embodiment, as shown
in FIG. 2A, the reinforcing ribs 20 are disposed between the linear stack
comprising two or more electrodes 12 and the compliant layer 16. In one
embodiment, as shown in FIG. 2B, the reinforcing ribs 20 are disposed
between the compliant layer 16 and the rigid outer housing 22. According
to another embodiment, the current collectors, when rigid, function as
current collectors and as reinforcing ribs. A reinforcing rib internal or
external to the shrink tube can enhance the mechanical robustness of the
packaged capacitive device.

[0037]The reinforcing rib material, in some embodiments, is selected from
a structural polymer, a metal, a ceramic, and a combination thereof. The
packaged capacitive device, in some embodiments, comprises two or more
reinforcing ribs axially disposed to the compliant layer.

[0038]According to some embodiments, as shown in the photographs in FIG. 3
and FIG. 4, the packaged capacitive device 300 and 400 respectively,
further comprises a first fluidic plug 28 (not shown in FIG. 4) adjacent
to a first end 24 of the linear stack and a second fluidic plug 30
adjacent to a second end 26 of the linear stack. In one embodiment, the
first fluidic plug comprises an inlet 32 for receiving a fluid and the
second fluidic plug comprises an outlet 34 for discharging at least a
portion of the fluid received by the inlet. In one embodiment, the inlet
and/or the outlet comprises a valve for regulating the flow of a fluid.
The first fluidic plug and the second fluidic plug can be sealed to the
linear stack by the compliant layer. The inlet and/or the outlet, in some
embodiments, are connectorized to allow attachment to a flow system.

[0039]Another embodiment of the invention is a method of making a packaged
capacitive device. The method comprises providing a linear stack
comprising two or more electrodes arranged in series, providing at least
two current collectors, each in contact with one or more electrodes in
the linear stack, wherein electrodes in contact with one current
collector are insulated from contact with another current collector, and
applying a compliant layer enclosing the linear stack, and the current
collectors. The two or more electrodes are electrically isolated from
adjacent electrodes in the linear stack, such that in an anode and
cathode array, adjacent electrodes do not short together. In one
embodiment, adjacent electrodes are isolated via a physical space. In
another embodiment, an electrically insulating material is disposed
between adjacent electrodes.

[0040]In one embodiment, applying the compliant layer comprises
diametrically expanding an elastomeric housing, positioning it around the
linear stack and the current collectors, and removing the expanding
forces and allowing the compliant layer to contract to apply radial and
axial compressive forces to the linear stack and current collectors. In
some embodiments, allowing the compliant layer to contract to apply
radial and axial compressive forces to the linear stack and current
collectors comprises applying heat to the compliant layer such that the
compliant layer shrinks and conforms to the shape of the linear stack and
the current collectors.

[0041]The method of making a packaged capacitive device can further
comprise attaching a first fluidic plug adjacent to a first end of the
linear stack and a second fluidic plug adjacent to a second end of the
linear stack. In one embodiment, the first fluidic plug comprises an
inlet for receiving a fluid and the second fluidic plug comprises an
outlet for discharging at least a portion of the fluid received by the
inlet. In one embodiment, the inlet and/or the outlet comprises a valve
for regulating the flow of a fluid.

[0042]According the methods described herein, a water-tight packaged
capacitive device may be achieved through the judicious use of mechanical
pressure, sealant, or careful material selection. Robust mechanical and
electrical contact between the electrodes and their like-signed current
collector can be achieved, while providing isolation from an
opposite-signed current collector.

EXAMPLE I

[0043]The packaged capacitive device shown in FIG. 3 comprises a linear
stack of 50 activated carbon electrodes, which are 25 mm in
diameter×3 mm in thickness. The electrodes were processed from a
phenolic resin-based extruded honeycomb cylinder, for example, similar to
those described in U.S. Pat. No. 6,214,204.

[0044]The electrodes in electrical contact with one current collector were
insulated from electrical contact with another current collector using an
electrically insulating compliant material. In this embodiment,
insulators and spacers made from Dow Corning Sylgard 184 were applied to
each electrode, covering approximately 180 degrees of the circumference
of each electrode. Each sequential electrode was rotated 180 degrees
about its cylindrical axis so that the silicone strips on adjacent
electrodes were diametrically opposed. These molded pieces provide
isolation for each electrode from the oppositely signed current collector
and isolation from the adjacent electrodes.

[0045]Fluidic plugs having a cylindrical shape were made from a machinable
engineering plastic and are 25 mm in diameter×mm in thickness. The
fluidic plugs were placed on each end of the linear stack. Both fluidic
plugs contain a drilled and tapped through hole containing a 1/4'' quick
connect tubing connector. Two strips of rolled exfoliated graphite sheet,
for example, Grafoil®, available from Graftech Inc. 175
mm×mm×0.05 mm were placed adjacent to the linear stack and
diametrically opposed with respect to each other. These strips act as
current collectors. Two strips of commercially pure titanium foil 30
mm×75 mm×0.25 mm were placed at each end of the capacitive
device, overlapping the Grafoil® sheets. These form the electrical
interface to the environment in the packaged capacitive device. Then a
180 mm in length piece of 30 mm in diameter FEP shrink tube was placed
over the linear stack, the current collectors, the titanium sheets, and
the fluidic plugs. The shrink tube was shrunk to conform to the linear
stack, the current collectors, the titanium sheets, and the fluidic plugs
using a heat gun with a nozzle air temperature of approximately
300° C. Heating continued until the tubing drew down tightly,
bringing the Grafoil® current collectors into mechanical contact with
the electrodes.

[0046]A stainless steel hose clamp was placed around each end of the
capacitive device and tightened. The hose clamps serve to achieve good
electrical contact between the titanium and the graphite sheet and to
help minimize fluidic leakage. 732 RTV sealant, commercially available
from Dow Corning, was applied to both ends of the device to further seal
against leakage.

EXAMPLE II

[0047]One embodiment of a packaged capacitive device according to the
invention is shown in FIG. 4. The capacitive device 400 comprises a
linear stack of 6 activated carbon electrodes arranged in series. The
carbon electrodes are 75 mm in diameter by 3 mm in thickness. The
electrodes were processed from a phenolic resin-based extruded honeycomb
cylinder, for example, similar to those described in U.S. Pat. No.
6,214,204. Strips of 3 mm thick silicone sheet were placed on the
electrodes, covering approximately 180 degrees of the circumference of
each electrode, and were bonded to the electrodes using 732 RTV sealant.
Each sequential electrode was rotated 180 degrees about its cylindrical
axis so that the silicone strips on adjacent electrodes were
diametrically opposed. Rings of 1 mm thick silicone sheet were placed
between adjacent electrodes to electrically isolate them from each other.
A first fluidic plug, in this embodiment, a disc of machinable
engineering plastic 75 mm in diameter×25 mm in thickness were
placed on each end of the linear stack. Both fluidic plugs contained a
drilled and tapped through hole containing a 1/4 inch quick connect
tubing connector. Two strips of Nickel foil 120 mm×30 mm×0.09
mm were placed adjacent to the electrode stack diametrically opposed with
respect to each other. Then a 120 mm long piece of 100 mm in diameter of
FEP shrink tube was placed over this stack of components and shrunk to
conform using a heat gun having a nozzle air temperature of approximately
300° C. Heating continued until the tubing drew down tightly onto
the stack, bringing the Nickel foil current collectors into mechanical
contact with the electrodes.

[0048]It will be apparent to those skilled in the art that various
modifications and variations can be made to the present invention without
departing from the spirit or scope of the invention. Thus, it is intended
that the present invention cover the modifications and variations of this
invention provided they come within the scope of the appended claims and
their equivalents.